The interspinous ligament of the lumbar spine - Magnetic resonance images and their clinical significance

Study Design. A preliminary study of magnetic resonance features of the int erspinous ligament in degenerative lumbar spine. Objectives. To classify the magnetic resonance imaging features of the inte rspinous ligaments in relation to the patient's age, disc degeneration, and radiographic instability. Magnetic resonance imaging also was correlated w ith the histologic findings of the interspinous ligaments. Summary of Background Data. As reported, rupture of the interspinous ligame nt frequently is found in the degenerative lumbar spine. However, little in formation is available in the literature on imaging assessment of the inter spinous ligament in degenerative lumbar disorders. Methods. In this study, 24 interspinous ligaments at L1-L2 or L2-L3 from 15 patients with nondegenerated discs were selected to represent normal magne tic resonance features of the interspinous ligament, and 38 patients with t he mean age of 49 years underwent functional radiography and magnetic reson ance imaging. The magnetic resonance features of the interspinous ligament were classified into five categories according to their signal intensities: Type 1A (low intensity on T1- and T2-weighted images without hypertrophy o f the spinal process); Type 1B (same signal pattern as in Type 1A with hype rtrophy of spinal process); Type 2 (low intensity on T1- and high intensity on T2-weighted images); Type 3 (high intensity on T1-weighted images); and Type 4 (others). Seven patients with variable patterns of the interspinous ligament were selected to undergo histologic examinations. Results. Of the interspinous ligaments considered normal, 80% were classifi ed as Type 1A. There were 14 Type 1A, 30 Type 1B, 19 Type 2, 16 Type 3, and 20 Type 4 ligaments. The mean age and disc degeneration grade of the patie nts with the Type 1B ligaments was significantly higher. Instability was fo und to be associated with Type 2 interspinous ligaments (7 of 19), whereas instability rarely was noted in Types 1A (1 of 14) and 1B (1 of 30) ligamen ts. The histologic examination revealed that chondrometaplasia and necrotiz ation of fiber bundle predominated in Type 1B, proliferation of cells and v ascular invasion in Type 2, fatty degeneration in Type 3 ligaments. Conclusions. The magnetic resonance imaging characteristics may be helpful in assessing normal or pathologic changes in the interspinous ligaments.